Zirconium oxide ceramics have been widely used in the production of dental prostheses due to the good biocompatibility and excellent mechanical properties.
Before zirconium oxide ceramics are finally produced to be a dental prosthesis that can be used for patients, they generally need coloring, glazing processes and the like to ensure the color of finally produced dental prosthesis is close to the tooth color of the patients themselves.
In the prior art, there are mainly two methods for coloring the zirconium oxide ceramics. The first method is adding coloring oxides to the raw materials during the process of preparing zirconium oxide ceramics, thus obtaining the pre-shaded zirconium oxide ceramics. The second method is using coloring liquid to color the restorations of the patient, which is made from zirconium oxide pre-sintering body. The natural tooth shows a narrow range of color variance, and mainly appears to be red or yellow. Thus, no matter the colorant is the coloring oxide of the first method or the coloring agent of the second method, the contained coloring ions in which mainly contain Fe3+, Er3+, and Mn2+ etc., wherein Fe3+ is mainly for deepening yellow and red, Er3+ is mainly for deepening red, and Mn2+ is mainly for adjusting lightness. Since the radius and coordination number of Fe3+ ion is different from those of Zr4+, most of Fe3+ ions in the zirconium oxide ceramics exist in crystal boundary, such that the transparency of the colored zirconium oxide ceramics will reduce tremendously.
Replacing Fe3+ in the above-mentioned ions with Pr3+ can increase the transparency of the colored zirconium oxide ceramics. However, coloring zirconium oxide ceramics by Pr3+ instead of Fe3+, after glazing and firing the colored zirconium oxide ceramics, it appears obviously lighter yellow compared with that before firing. Sometimes, porcelain veneering and the first firing are needed according to the requirement of the colored zirconium oxide ceramics; then glazing and the second firing are performed. In this way, after firing for several times, it allows the zirconium oxide ceramic to exhibit a much lighter yellow. Thus, Fe3+ cannot be completely replaced with Pr3+ for coloring zirconium oxide ceramic to be yellow at the present stage.